The invention relates to a method for producing spring rails made of steel, in particular for windshield wipers having a rubber or elastomer wiper blade.
Conventional windshield wipers for automobiles include a wiper arm which is supported on a wiper shaft and are driven by a wiper motor. A spring rail with a wiper blade made of rubber is arranged at the end on the wiper arm and frequently attached in an articulated manner. The wiper blade has a wiper edge used to remove water and/or dirt adhering to the windshield.
For a satisfactory function of the wiper blade, the wiper edge should move during operation across the generally curved windshield with constant pressure. The curvature of the spring rail and therefore also the curvature of the wiper edge should adjust themselves under operating conditions so as to contact the windshield to be cleaned across its entire length, in particular, however, at the ends, with sufficient pressure.
In particular at high vehicle speeds, wind turbulences frequently reduce a constant pressing force across the entire wiper length, in particular where the windshield has greater curvature.
In order to maintain the pressure of the wiper blade even at high vehicle speeds and/or wind speeds, the wiper blade must be pressed against the windshield by the spring rail. For example, it is known to insert one or two spring rails into lateral grooves or centrally into the wiper blades.
Due to the spring-elasticity of the spring rail, oscillations may occur, in particular characteristic or resonance oscillations, which may cause the wiper edge to partially lift off, thereby significantly reducing the visibility through the vehicle windshield.
To improve the oscillation characteristic of wiper blades, the published PCT application WO 01/58731 A1 proposes to employ two spring rails which have different resonance frequencies from each other as a result of their different width or thickness or also as a result of their material composition. This is supposed to result in a quieter wiper operation. Disadvantageously, however, the oscillation characteristic is only reduced for a few fixed frequencies, so that the changing operating and oscillation behavior in practical applications cannot be satisfactorily eliminated. In addition, using the different spring rails requires complex assembly and also increases inventory costs.
The elastic oscillations which are undesirable in windshield wipers are generally caused by the low damping of the spring steels used for the spring rails. The reason is that only very few processes that dissipate energy take place in the steel. This is disadvantageous and unfavorable with windshield wipers, because it can cause rattling. Rattling may severely interfere with the operation, reduce the service life of the wiper rail and also present a safety risk.
Investigations have shown that the oscillation characteristic of spring rails in windshield wipers can be dampened by the rubber of the wiper blade. However, this is satisfactory only if a very tight positive contact or a connection exists between the rubber of the wiper blade and spring rail—at least locally at certain locations. Inserting the spring rail into recesses or guide channels of the wiper blade, however, does generally not produce sufficient damping of oscillations, because the spring rail—even when embedded—still has degrees of freedom for oscillations. In practice, this can cause relative movement between the spring rail and the wiper blade, thereby preventing uniform wiping at high vehicle speeds or during wind turbulences. This results in undesirable and detrimental rattle oscillations which have a negative effect in particular at high vehicle speeds.
The invention intends to eliminate these disadvantages and proposes to use a multilayer-coated spring element as a spring rail for windshield wipers. In addition, it should be possible to process the spring rail together with the wiper blade non-positively into a composite part in a simple and cost-effective manner, without requiring punched openings for affixing the spring rail.
It is therefore also an object of the invention to construct the surface of the spring rail so as to enable a non-positive connection to the wiper blade.